Other than using Google one with backup I don’t know of any app to backup the Full android watches.
For safety sake the apps that I use which store data are ones that have web based storage on servers, (my diet app, diabetes app, blood pressure app, all my google apps like mail, notes, etc.)
for the apps themselves I have a list of the ones I use to download from play store. I keep APK files for the apps not on play store on google drive or drop box.
It isn’t pretty but, when my LEM14 passed away I was able to rebuild the new one in an hour. I can also follow the same process to configure my other watches to have the same set up.